1. An Integrin Binding-defective Mutant of Insulin-like Growth Factor-1 (R36E/R37E IGF1) Acts as a Dominant-negative Antagonist of the IGF1 Receptor (IGF1R) and Suppresses Tumorigenesis but Still Binds to IGF1R*
- Author
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Masaaki Fujita, Jane Q. Chen, Robert D. Cardiff, Alexander D. Borowsky, Yoko K. Takada, Yoshikazu Takada, Machelle D. Wilson, Dora M. Cedano-Prieto, Mac H. Wu, Katsuaki Ieguchi, Charles Wilkerson, Andrew Fong, Anthony T.W. Cheung, and Su Hao Lo
- Subjects
endocrine system ,Integrins ,Cell Survival ,medicine.medical_treatment ,Mutation, Missense ,Biology ,Biochemistry ,Models, Biological ,Receptor, IGF Type 1 ,Insulin-like growth factor ,Mice ,Cell Line, Tumor ,medicine ,Animals ,Humans ,Insulin ,Viability assay ,Insulin-Like Growth Factor I ,Protein Structure, Quaternary ,Molecular Biology ,Ternary complex ,Integrin binding ,Insulin-like growth factor 1 receptor ,Cell Biology ,Molecular biology ,body regions ,Insulin receptor ,Cell Transformation, Neoplastic ,Amino Acid Substitution ,Cancer cell ,biology.protein ,NIH 3T3 Cells ,Signal transduction ,hormones, hormone substitutes, and hormone antagonists ,Signal Transduction ,Protein Binding - Abstract
Insulin-like growth factor-1 (IGF1) is a major therapeutic target for cancer. We recently reported that IGF1 directly binds to integrins (αvβ3 and α6β4) and induces ternary complex formation (integrin-IGF1-IGF1 receptor (IGF1R)) and that the integrin binding-defective mutant of IGF1 (R36E/R37E) is defective in signaling and ternary complex formation. These findings predict that R36E/R37E competes with WT IGF1 for binding to IGF1R and inhibits IGF signaling. Here, we described that excess R36E/R37E suppressed cell viability increased by WT IGF1 in vitro in non-transformed cells. We studied the effect of R36E/R37E on viability and tumorigenesis in cancer cell lines. We did not detect an effect of WT IGF1 or R36E/R37E in cancer cells under anchorage-dependent conditions. However, under anchorage-independent conditions, WT IGF1 enhanced cell viability and induced signals, whereas R36E/R37E did not. Notably, excess R36E/R37E suppressed cell viability and signaling induced by WT IGF1 under anchorage-independent conditions. Using cancer cells stably expressing WT IGF1 or R36E/R37E, we determined that R36E/R37E suppressed tumorigenesis in vivo, whereas WT IGF1 markedly enhanced it. R36E/R37E suppressed the binding of WT IGF1 to the cell surface and the subsequent ternary complex formation induced by WT IGF1. R36E/R37E suppressed activation of IGF1R by insulin. WT IGF1, but not R36E/R37E, induced ternary complex formation with the IGF1R/insulin receptor hybrid. These findings suggest that 1) IGF1 induces signals under anchorage-independent conditions and that 2) R36E/R37E acts as a dominant-negative inhibitor of IGF1R (IGF1 decoy). Our results are consistent with a model in which ternary complex formation is critical for IGF signaling. Background: The integrin binding-defective mutant of IGF1 (R36E/R37E) is functionally defective and does not induce ternary complex formation (integrin-IGF1-IGF1R). Results: R36E/R37E suppressed signaling induced by WT IGF1, the binding of WT IGF1 to cells, ternary complex formation, cell viability, and tumorigenesis. Conclusion: R36E/R37E is a dominant-negative antagonist of IGF signaling. Significance: R36E/R37E has potential as a therapeutic agent.
- Published
- 2013